In the conventional art, a magnetic recording medium using a longitudinal magnetic recording system is well known. On the other hand, in order to respond to the demands for future increases in the recording density of magnetic recording media, a perpendicular magnetic recording system is drawing attention as an alternative system to a longitudinal magnetic recording system. The perpendicular magnetic recording medium is mainly composed of a magnetic recording layer which is magnetized in the nearly perpendicular direction, an under layer which orients the magnetic recording layer perpendicular direction, and a protective layer which protects the surface of the magnetic recording layer. In addition, a soft magnetic undercoat film comprising a soft magnetic material which has a role in concentrating the magnetic flux generated by a magnetic head used for the recording in a magnetic recording layer is optionally additionally provided.
Increase in the recording density is required in perpendicular magnetic recording media as well as in longitudinal magnetic recording media. These are essential to be compatible with the reduction of noise with high thermal fluctuation resistance in order to achieve increase in recording density of the magnetic recording medium. That is, the fine crystal grain size of the magnetic recording layer should be reduced to reduce noise and the magnetic interaction between the magnetic grains should be reduced while increasing the crystal magnetic anisotropy Ku in order to increase the thermal fluctuation resistance.
In order to combine the decrease of noise and high thermal fluctuation resistance, various components, structures, materials and other solutions of a magnetic layer and an under layer were proposed conventionally. In particular, in recent years, a magnetic recording medium using a granular magnetic layer surrounded by a grain boundary region such as nonmagnetic oxides or nitrides are proposed (refer to, for example, Japanese Unexamined Patent Application, First Publication No. Hei 07-311929 and Japanese Unexamined Patent Application, First Publication No. 2002-15417).
The magnetic interaction between the magnetic grains is reduced by segregation of Cr to the grain boundary by producing the conventional Cr segregation type CoCr based alloy magnetic film at high temperature. However, it was difficult to form a grain boundary region of Cr alone by segregating Cr sufficiently from inside magnetic grains since Cr is partially solidly dispersed with Co. On the other hand, in the case of a granular magnetic layer, there is an advantage in that the granular magnetic layer easily segregates nonmagnetic compound which is immiscible with Co more than the conventional film of CoCr based alloy magnetic film does and the isolation of the magnetic grains is accelerated comparatively easily since a nonmagnetic compound which is non-solid-dispersible with Co is used as a grain boundary region.